Concern over COVID-19 infections is being compounded by the earlier-than-usual start to Japan's flu season, with prefectures and schools grappling with influenza outbreaks as health ministry reports show higher numbers week by week.

In the period between Sept. 11 and 17, the average national influenza case count rose to over 7.03 per medical institution from just 4.48 the week prior, according to the health ministry's most recent weekly report released Friday.

Overall, 34,665 cases were reported, compared with just 111 during the same period last year. The previous week, the ministry's reported overall case count was 22,111.

Okinawa Prefecture had the highest average count with over 20 cases.

The quick rise in cases over the past few weeks has triggered an “influenza advisory” by the prefecture for the first time in four years, after the count surpassed the advisory issuance threshold of 10 cases. During the week through Sept. 10, the average count was 13.43, with young people accounting for around 75% of cases.

Following Okinawa were Ehime, Saga, Chiba and Tokyo prefectures.

Tokyo also issued an influenza alert last week after surpassing the 10-case threshold, reaching 11.37. At her regular news conference on Friday, Tokyo Gov. Yuriko Koike encouraged continuing infection prevention measures, such as proper ventilation, handwashing and mask-wearing, to prevent both the flu and COVID-19.

“This (figure) suggests a high likelihood of a significant outbreak occurring within the next four weeks,” Koike said.

The number of schools affected by outbreaks of influenza-like symptoms is rising week-by-week across the country, according to the health ministry. Elementary schools continue to be most affected.

Between Sept. 11 and 17, over 2,400 schools decided to either suspend individual classes and grades or to close school facilities altogether. Forty-eight schools reported whole facility closures, compared with just 10 the week prior.

While national COVID-19 cases were down from the week prior, the coronavirus continues to be prevalent.

For the week between Sept. 11 and 17, 86,510 cases of COVID-19 were reported, with an average case count of 17.54 per reporting institution, down from over 20 the week prior.

The fall COVID-19 vaccine rollout began last week, and the health ministry recommends checking municipal guidance on distribution plans.

COVID-19 vaccines are currently free of charge, while the cost of influenza vaccines can differ by medical institution.